A New Dawn for Vesta

NASA’s Dawn spacecraft obtained this image of the giant asteroid Vesta with its framing camera on July 9, 2011. It was taken from a distance of about 26,000 miles (41,000 kilometers) away from Vesta, which is also considered a protoplanet because it is a large body that almost became a planet. Each pixel in the image corresponds to roughly 2.4 miles (3.8 kilometers). Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

On July 15, NASA’s Dawn spacecraft began a prolonged encounter with the asteroid Vesta, making the mission the first to enter orbit around a main-belt asteroid.

The main asteroid belt lies between the orbits of Mars and Jupiter. Dawn will study Vesta for one year, and observations will help scientists understand the earliest chapter of our solar system’s history.

Engineers expect that the spacecraft was captured into orbit at approximately 10 p.m. PDT Friday, July 15 (1 a.m. EDT Saturday, July 16). They will hear from the spacecraft and confirm that it performed as planned during a scheduled communications pass that starts at approximately 11:30 p.m. PDT on Saturday, July 16 (2:30 a.m. EDT Sunday, July 17). When Vesta captures Dawn into its orbit, engineers estimate there will be approximately 9,900 miles (16,000 kilometers) between them. At that point, the spacecraft and asteroid will be approximately 117 million miles (188 million kilometers) from Earth.

"It has taken nearly four years to get to this point," said Robert Mase, Dawn project manager at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. "Our latest tests and check-outs show that Dawn is right on target and performing normally."

Engineers have been subtly shaping Dawn’s trajectory for years to match Vesta’s orbit around the Sun. Unlike other missions, where dramatic propulsive burns put spacecraft into orbit around a planet, Dawn will ease up next to Vesta. Then the asteroid’s gravity will capture the spacecraft into orbit. However, until Dawn nears Vesta and makes accurate measurements, the asteroid’s mass and gravity will only be estimates. So the Dawn team will need a few days to refine the exact moment of orbit capture.

NASA’s Dawn mission will visit two of the first bodies formed in our solar system: the "dwarf planet" Ceres and the massive asteroid Vesta. Credit: NASA

Launched in September 2007, Dawn will depart for its second destination, the dwarf planet Ceres, in July 2012. The spacecraft will be the first to orbit two solar system destinations beyond Earth. Studying both Vesta and Ceres will help astrobiologists understand how small bodies formed and evolved in our solar system. Determining the physical properties of Ceres and Vesta can also help us determine if objects from the astroid belt could have played a role in delivering materials to the early Earth that played a role in the origins of life.

Dawn’s mission to Vesta and Ceres is managed by JPL for NASA’s Science Mission Directorate in Washington. Dawn is a project of the directorate’s Discovery Program, which is managed by NASA’s Marshall Space Flight Center in Huntsville, Ala. UCLA is responsible for overall Dawn mission science. Orbital Sciences Corp. of Dulles, Va., designed and built the spacecraft. The German Aerospace Center, the Max Planck Institute for Solar System Research, the Italian Space Agency and the Italian National Astrophysical Institute are part of the mission team.